In recent years the problem of the molecular organization of biological membranes and the relations between structure and physiologically important membrane properties have been the focal point of intense research activity. This activity has been generated by the realization that, within the cell, the membrane occupies a position of central importance among the organizational asssemblies which comprise much of the basic cellular machinery. Because of this central position, defects in membrane composition and structure which result in altered properties can give rise to such diverse pathological conditions as demyelination in the central nervous system, renal tubular failure and certain hemolytic anemias. The research proposed in this application is carried out with the objective of obtaining basic information upon which can be built an understanding in molecular terms of physiologically important phenomena associated with biological membranes. Work is centered on the continuing investigation of the relations between the properties and molecular structure of lipid bilayer membranes and derivative systems formed by interaction of the bilayer with synthetic molecules and with isolated, purified functional components of biological membranes. This approach is based on the premise that much of the lipid in cellular membranes is present in bilayer form and as such constitutes a barrier matrix for the organization of functionally important protein and carbohydrate components.